Telephone-exchange system



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L H JOHNSON TELEPHONE EXCHANGE SYSTEM F'lled Augusl 21 1925 N Dec. 29 1925.

/nvenar Lew/5 #Johnson by f a www 1,567,271 L H JOHNSON TELEPHONE EXCHANGE SYSTEM Filed August 21, 192:. 4sheets-sheet 2 Dec. 29 l925 Hg. a

Dec. 2 9, 1925- 1,567,271

L.. H. JOHNSON TELEPHONE EXCHANGE SYSTEM Filed August 21, 1923 4 Sheets-Sheet 5 L. H. JOHNSON TELEPHONE EXCHANGE SYSTEM Filed August 21, 1923 4 Sheets-Sheet 4 Patented Dec. 29, 1925.

UNITED STATES PATENT OFFICE.

LEWIS I-I. JOHNSON, OF MADISON, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application led August 21, 1923.

To all whom t may cof/wem:

Be 1t known that I, Lewis H. JOHNSON,

i a citizen of the United States of America,

residing at Madison, in the county of Morris, State of New Jersey, have invented certain new and useful Improvements in Telephone-Exchange Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to an exchange systemV and more particularly to a system in which connections are established between subscribers lines by means of automatic selector s fitch mechanism.

In large exchange areas comprising a number of offices, certain of the oliices may be remotely removed from each other. 1Where oflices are located in the saine dis- `trict of the area, direct trunking facilities between the oflices so located is desirable and economical. If, however, offices are quite remote from each other, as certain of them would be in alarge area, the provision of direct trunking facilities of sufficient capacity to handle the peak load would not be economical since the cables would be long and during a large portion of the time, particularly at night, would be employed at onlyra'small percentage of their capacity.

One method of routing inter-ofce connections in large machine switching areas between remotely located offices has been proposed. This proposal employs an intermediate Oiiice as tandem point. Thus, the connection between two remote points A and C would first be built up from point A to B and then treated at B as a connection initiated at that point and built up from B to C. This is accomplished by setting up a complete oce and line designation of the wanted line in a central oiiice sender at point A, extending the connection to point B under the control ofthe sender in accordance with the office designation of the line, then transferring theV complete officeY and line designation from the sender at point A to a register sender at point B. The sender at point B then controls the setting of switches thereat to extend the connection to the point C and to the Wanted line terminating at thatv point. This inffentien hasl been disclosed in one of its as- Serial No. 658,512.

pects in the copending application of YV. L. Dodge, Serial No. 482,189, tiled June 22, 1920.

Another method of accomplishing interoilice trunking in accordance with the present invention obviatcs the necessity of transferring the sender setting from the originating point to the intermediate point by establishing a connection directly from the district selector frame of the originating point to the oliicc selector frame of the intermediate point, the o'llice selector of the intermediate point being then directly controlled by the sender at the originating point to extend the connection to the point in the exchange area where the wanted line terminates. Thus, the district selector of the originating point and the office selector of the intermediate point operate conjunctively in accordance with the office designation of the wanted line.

lnorder, however, that the utmost economy in cable investment may be realized, it is desirable that the office selector of the intermediate point to which the district selector of the originating point has access be arranged for operation over a two wire interoffice loop rather than over the three- Wire circuit customarik employed between district selector and otlice selector frames.

It is, therefore, an object of the present invention to provide an office selector which may be controlled either locallyY from a sender in the same oice therewith or remotely from a sender in a distant office, efliciently and economically.

It is a further object of the invention to provide means for extending connections between remote offices of an exchange area with the greatest possible economy of trunking and apparatus facilities.

It is a further feature of Jthe invention to provide means individual to a selector switch for changing the resistance of the control circuit thereof during different stages of the operation of the switch.

These and other objects of this invention are accomplished by providingl an ottice selector, all of the functions of which may be controlled over two-wire trunk-loops leading thereto and therefrom, provision being made to automatically advance the selector l scribers line Cy terminates.

and restore it upon its failure to function in response to the ordinary control within a predetermined period.

It is thought that the invention will best be understood from a consideration of the circuits in detail land the manner in which the f function. Referring'to' the drawings Fig; 1 shows the line of a subscriber A terininating in an originating oiiice V of the exchange area, the schematic representation of a line switch and sender selector by means of which the line may become associated with a central ofiice lregister sender, such portions of a registeisender 'shown'in the lower portion of Fig. 1 as are necessary to an understanding of the invention and the schematic -representation of` a districtvvd selector by means of which lthe Aline maybe further eX- tended. Above the dotted line in the upper portion of Fig. 1 the line of a second subscriber D, lineswitch, district selector and ksender 'ofj another otiice VW of the exchange eration "on a call'indicator basis and func-Y tions with the call'i'ndicator shown in Figi 4i.V

' F-igfi'shows as much of a relay call indiclatormechanism for functioning in conjunction with the 'trunk circuit'of Fig. 3 as is necessary to an understanding of the invention.

i For acoinplete disclosure of the invention, they several iigures of the drawing should be arranged ywithv Fig.'2 at the jright of Fig. f 1,-`Fig. 3 at the right of F ig.y 2 and e beneath Fig. 3 with the linesv extending to the margins of the several figures in alignment.

Tire/"selector switches and oiiice senders indicated in Figui andthe upper portion of Fig. 3 may be'of identically lthe saine type and 'function in the saine` manner as the simi- "larapparatus disclosed and, .described in detail in the PatentNo. 1,505,171, issued to F. A. Stern, August '19, "1924. Only such portions of these switches land senders'have "been disclosed he'reinlas are considered necessary to an understand-ing of the invention,

reference 1being -ina'de herein' to'the above videntiiied patent for a full detailed disclosure. v Y p The selector switch shown in Fig. 2`inay be of the general type disclosed in the patent now be assumed that the subscriber whose 08e, issued to A. ELundell and Eil-. Clark,

August 7, 1923. Only such portions of the call indicator circuits have been disclosed herein as are necessary to an understanding of the invention.

The apparatus to be employed having now been described in a general manner, it will line is indicated at A of oiiice V, Fig. 1, de-' sires a connection with a subscribers line B in the full mechanical office Y, Fig. 3,' and no direct trunking facilities existing between these oces, it is necessary to route the connection through the oiiice selector of the intermediate office X. TheV subscriber A upon initiating the call removes his receiver from the switchhoolr., thereupon causing the setting of the brushes of the line switch 101 upon a district selector link terminating in a district selector 102. Then the district link circuit is seized by the line switch, the sequence switch associated therewith (not shown) advances to position 2 in 9') which the sender selector SS functions to associate an idle sender with the subscribers line. It will be assumed that the sender shown in the lower portion of Fig. 1 is idle and becomes associated with the calling line, whereupon a pulsing circuit is established from battery through the-pulsing relay 10S, wiper 107 the lower right contact of vcam 104, thellower brush of line switch 101, over the subscribers line loop, returning over the upper brush of switch 101, the lower con-l tact of cam 108, wiper 105 to ground through balancing coil 106. As soon as this pulsing circuit 'is established, the calling subscriber receives the usual dialing tone and pro- 110 ceeds to dial the digitsof the wanted line designation, thereby setting the registers of the `sender to record the oiiice and line designations of the wanted line.

set in the well known manner to select the trunk group extending to the intermediate oice X, it being assumed that it is necessary to extend the connection through this intermediate ofiice in order to reach the ter-miiiatiiig office Y in which the wanted line terminates. Following the selection of the proper trunk group, the district selector 102 :functions to select an idle trunk in the group Such as the one indicated at 109, 110. As soon as the district selector terminates its trunk hunt-ing operation, the sequence switch associated with the district link advances in the well known manner to position 10 whereupon a fundamental circuit is cstalolishctl over the conductors of the inter-office trunk for controlling the office selector 250 at the ofhce X. This fundamental circuit may be traced from battery, the right contact of cam 201, winding of control relay 202, lower contact of cam 203 compensating resistance elements 20a and 205, the lower lett and upper right contacts of cani 20G, outer right back contactof relay 207, conductor 109, uppermost brush of switch 102, lower Contact of cam 111, wiper 112, cam contact 113 of the sender control sequence switch 114, lower contact of cam 115, winding of sender stepping relay 110, back contact ot the 0 counting relay 117, lower contacts of cam 118, associated with the ollice sender i sequence switch (not shown), contact of cam'119, wiper 120, right contact or cam 121, lower brush of switch 102, trunk conductor 110, inner right back contact oi relay'207, upper left and lower right contacts of cam 208, compensating resistance elements 209 and 210 to ground at the left contact of cam 211.

Stepping relay 116 of the sender and control relay202 of the office selector operate in this circuit, relay 202 in closing a circuit over the lower contact of cam 212, to bat tery through the left winding of relay 213, and the stepping relay 116 of the sender preparing the usual control circuits for controlling oiiice brush selection in accordance with the setting of its office code registers. Relay 213 upon energizing loclis in a circuit extending through its left winding, left armature and front contact, upper left contact of cam 212 to ground at the armature contact of relay 202. At its right armature and 'front contact, relay 213 completes a circuit extending over the lower left contact of cam 214 to battery through the magnet winding of sequence switch 200 for advancing the sequence switch into position 2. lVith the sequence switch `200 in position 2 and relay 213 energized, a. circuit is estab lished for the updrive magnet 215 extending from battery through the. winding ot this magnet, the lower right Contact of cam 216 to ground at the right armature and front contact of relay 213. The brush shaft is thereupon driven upwardly in its brush selection movement. As it approaches its iirst brush selection position, the shaft wiper 217 engages the lowermost conducting portion of commutator segment 218 whereupon a circuit is closed in shunt of the winding ot the sender stepping relay 116, which shunt circuit may be traced from battery, right contact of cam 201, winding of relay 202, right contact of cam 203, conductor 21S), segment 218, wiper 217, thence to ground at the lower right contact of cani 220. Upon the establishment of this shunt circuit, the sender stepping relay deenergizcs and in the well known manner causes the opera-- tion of a pair of counting relays.

As the brush shalt continues its upward morcifnent, thc wiper 21T encounters a noncenducting portion of commutator segment 218 and the previously traced shunt circuit is opened` again permitting the energication of relay 116. Thus, as the brush shaft continues to advance, the stepping relay 11G intermittently shunted until the sender is satislied with respect to its othce brush regisi tration whereupon the 0 counting relay 117 cnergizes, opening the fundamental circuit, permitting the dcenergization of relays 11G and itt the otlice sender, preparation is thereupon made for controlling oiiice group selection. At the ottico selector, relay 202 iollowi g the opening of its circuit at the otlicc sender is maintained energized over the shunt circuit previrnisly traced until the shaft wiper 217 engages the next non-con ducting portion of the comn'iutator segment 21S, when the selected hrush will he aclay 202 deenergises, opening the locking circuit of relay 21S, which thereupon deenergizes, opening the circuit of updrive inagnet 215 to arrest the upward movement of the switch shaft. At the back contact of its right armature rela 218 establishes a' N circuit over the upper left contact of cam 21st for advancing sequence switch 200 out o't' position 2 into position 3.

vWhen sequence swltch 20() is iu position 3 and the oi'licc sender prepared for conf.

trol`lin5, l oll'ice group selection, the previously traced fuiulan'icntal circuit is again est-ah` lished through thc windings of relays 110 and 202, relay 202 again establishing the circuit 'lor relay 2li-l, which locks as before. lilith the sequentA 'mitch in position 3 and hffire it is advanced to position et hy the cnergization ol relay 215i, a circuit is estalilished 'l'or the trip magnet iii. e.'\;tcn ,ling from battery through the winding ol this magnet to ground over the upper right contact of cam 211. 'Whew thereafter, sequence switch 200 advances to position fl; under the control of relay 2153. the circuit of updrive magnet 215 estahlishcc as hein; d l.#-rilicil and the switch shaft is again driven ui wardlji'. The trip magnet 221 causes the trippingl ot the selected set ct' brushes.

its the switch sliaft continues in its upvfard mow-nient, the wiper engages the iso "lowermost conducting' portion of Vcommutator segment 223, whereupon, a circuit 'is closed in shunt of the sender stepping relay 116 which `may he traced as hefore'through the winding of relay 202, upper left Contact of cam 203, conductor 224, segment 223, Awiper 222, upper contact of cam V216 to ground at the right armature of relay 213. The sender stepping relay 116 thereupon deenergizes, causing the operation of a pair l'of-counting relays at the sender in the well linown manner. Upon the continued moyementof the brush shaft, the wiper 222 engages a non-conductingportion of commutator'223, and the shunt circuit is opened, permitting the rcenergization of relay 116. Thus,y as the switch shaft continues in its upward'movement the stepping 116 is intermittently 'operated until the Solider is satisffiedwith respect to its oiice group selection registration, when the counting relay 117 operates, opening the fundamental circuit and releasingrelay 116. Relay 202 is, how- ,ever,-"niaintained energized over the shunt circuit through the connnutator segment 223' 'funtil theselected brush' set has been moved toa position in which it enga-ges the first set of terminals in ythe vselected group. Vhen this position is lreached, the shaft wiper 222 engages a non-conducting portion of segment 223'and'relay 2027thereupon deenergizes. Vihen relay-y 202 ldeenergizes,V the holding circuit of relay 213 is opened and the circuit ofupdri'vev magnet 215 is in turn 'opened atfthev front contact of relay 213. lt/Vith relay 213 'deenergizech a circuit isfes- -tablished' over the upper left contact ofcam 214' for advancing"sequence switch'200 out ofz position 4-into position 5.

'Vith-sequenceswitch 200 in position 5, relayy 2131loecoines energized over its right vwinding and the upper right contact of cam 228, and at its right armature and front contact closes the circuit over the lower left contact of cam 214 for advancing se-A quence switch 200 into position 6. 1f the first trunk of the selected group is idle, re- `vlay 213 deenergizes as soon as vsequence switch 200 leaves position 5%. v If, however, thel rst trunk is busy, relay 213 becomes locked in position 5 of sequence switch 200 over its* left winding, left armature and rfront contact, lower right contact Yof cam 231, overflow segment 246 of the switch coinmutator, shaft wiper'247, test brush 230v and Ythence toground o-n the. test terminal of the first trunk.

'213 is maintained energized and a circuit is therefore established for thev updrive mag- Thus when sequenceswitch 200 advances into position 6, relay' search of the-terminal ofan idle trunk'in Vtest brush 230 van-d relay 213 deenergzes,

opening the circuit of the updrive magnet 215 and arresting the upward movement-of the switch shaft. Until the vlorush set is properly centered on theterminals of the 'selected idletrunk, relay 213, is maintained energized over the upper contactsof cam 232, conductor 263, commutator 'segment 226, shaft wiper 227,\upper contact of cam 216 to ground/at the right armature and front contact of relay 213. Upon the deenergization of relay`213 a circuit is closed at its rightarmature and hack contact over the upper left contactof cam 214 for advancingsequence switch 200 into the selection beyond position 7. I Relay 213 also at thehacl contact of its left armature'places-busy ground potential on the testterminalof the selected trunk over the brush 230, shaft wiper 247, commutator segment 246, lower right con-tact of cam 231,left'armatureandfback Contact yof relay 213, to ground' -at the lower left con -tact of cam 220. ris-soonJ assequence switch 200 advances into` position 6%, this 'lousy ground: potential is supplie-d independently of the relay 213 over the'upper right contact of cam 220. Y

`VVhilet-he sequence switch-"200" was in position 5a circuitwvas established from vloatteryl through the winding of relay 207, fthe lower left contact of cam 201, winding of relay 202, lower contact of-cam203,

--winding ofspolarized marginal relay 233 to -ground at theupper Aleft Contact of" cam 220.` The current fiowing througlrthe windfing of relay 233 isina direction-"which will not operate relay-i233fhut `placesit in con- 'ditionv towithstand cur-rents on Awhich it must Inot operate during thecontrol ofthe setting ofVH the 'remaining selector switches employed-inA thegestahlishinent of the'connection. Relays`207 -and`202, however, operate in this circuit and `arelo'clred over a circuit' traced through their windings, thence through resistance 234 to groundv at the armatureand'contact of relay 202,1as-soon l'as sequence switch 200 reaches position 6.

This lockingcircuit isniaintained through the selecti'onfheyond position 7 With relay l207 energized the fundamental circuit is extended from trunk'conductors 109 and 110 to the incoming 'selector 350, the tip side of the fundamental? circuit being traced from conductor 109, the outer right armature and front contact of relay 207, the lower left and upper right contacts of ca1n208, coinpensating resistance element210, the upper left and lower right contacts of fcam 235, brush 236, conductor 237, .the lower contact Cil of cam 300, resistance element 301, the right contacts of cam 302 to battery` through the winding of control relay 303 of the incoming selector. The ring side of the fundamental circuit may be traced from conductor 110 through inner right armature and front con tact of relay 207, the upper left and lower right contacts of cam 206, resistance element 204, the winding of relay 233, the right con tacts of cam 238, brush 239, conductor 241, upper contact of cam 304, resistance element 305 to ground at the lower contact of cam 306. The stepping relay 116 of thc sender an-d the control relay 303 of the incoming selector operate in this circuit. The current flowing through polarized relay 2 33 is not in the proper direction to cause its operation.

Under the control of the sender, the brushes of the incoming selector' 350 are set to select a final selector 360 having access to the terminals of the wanted line B. Following the setting of the incoming selector, the sequence switch associated therewith, not shown, advances to the selection beyond position 8, whereupon the fundamental circuit is extended for controlling the setting of the linal selector switch 360. During the setting of the final selector, the control relay 303 of the incoming selector' is maintained energized over a circuit which may be traced from battery through its winding, the lower contacts of cam 302, the armature and contact of relay 303, the lower right contact of cam 309, lower brush 303 of switch 350 to ground through the left contacts of cam 307. As soon as the last selection is completed at the linal selector 360 and the brushes thereof are set upon the terminals of the wanted line, the sequence switch associated with the linal selector advances beyond position 3%, thereby opening the circuit of relay 303. Relay 303, upon deenergizing advances the sequence switch of the incoming selector into position 9 in the well known manner. lith this sequence in position 9, conductors 237 and 241 are reversely connected to battery and ground for the purpose of advancing the sender at the originating` office into the talking selection position. Ground is connected to conductor 237 over the lower contact of cam 300, resistance element 301, contacts of cam 310 and through the lower contacs of cam 311, and battery is connected to conductor 2Ll1 over the upper contact of rain 30%, resistance element 305, lower contacts of cam 312 and through relav 303. f the advance of the sender, talking selee controlled at the district selector 102 in the well known manner.

rthis reversal of current in addition to advanc the sender and district link, causes the eriergization of polarized relay we at the selector 250. Relay :.33

upon energizing places a shunt around the winding of relay 202 which may be traced from the right terminal of relay 202 over the upper contact of cam 201 to ground at the armature and Contact ofV relay 233. Relay 202 thereupon deenergizes but relay 207, howev r, is maintained energized over the left contacts of cam 201 to ground at the armature and contact of relay 233. AS Soon as the sender advances from the units selection position preparatory to controlling talking selection, the fundamental circuit is opened permitting the deenergization of relays 233 and 303. Relay 233 thereupon opens the holding` circuit of relay 207. lVith relay 207 deenergized, trunk conductor 109 is connected over the outer right armature and back contactof relay 207 through the` right winding of relay 2110, the lower contacts of cam 235, brush 236, conductor 237, the lower contact of cam 300, resistance element 301, the right contacts of cam 302, the sequence switch of the incoming selector 350 having' advanced to position l() upon the deenergization of relay 303, thence to battery through the winding of relay 303. Truck conductor 110 is also connected over the inner right armature and back contact of relay 207 through the left winding of relay 2li-0, the upper contacts of cam 233, brush 239, conductor 241, upper' contact of cam resistance element 305 to ground at the lower contact of cam 306.

As soon as talking selection is started at the district selector 102, the pulsing circuit over wipers 105 and 107 of the sender sen lector is opened, and following the comple` tion of talking selection, the selected oilice sender is entirely disassociated from the established connection. The sequence switch of the district selector then establishes a talking circuit over the contacts of cams 111 and 121. At this time, the trunk conductors 109` and 110y are joined at the district selector over the upper contact of cam 111, through the windings of relay 122 and the lower contact of cam 121, thereby completing the circuit previously traced through the windings of relay 240 and the winding of relay 303 at the incoming selector. Rei lay 303 energizes in this circuit advancing the sequence switch of the incoming selector into the ringing position for ringing the called subscriber. Relay 240 also energizes closing a circuit from ground at its armature and front contact over the lower contact of cam 225 to battery through the left windingl of relay 213. Relay 213 thereupon encrgizes, closing a circuit over the lower' left contact of cam 214C and through the nir jnet winding of sequence switch 200 for .i ancing the sequence switch out of selection beyond position 7 into the talking position 10. As soon as the sequence switch leaves position 7, relay 21.3 deenergizes,

circuit is established betwleen the, calling Cil line A, and the calledlineB over the. ,conductors .shownnnyheavy lines 1n the .drawings, re-lay 240v being maintained energized euer-,the talkingfcircuit so long asV the con-V versation continues.

`When the conversationl is completed and the calling subscriberxrestores his -receiver to itsswitchhook theline switch101f and the district selector 102; areI released in ,the well known manner. Upon the release of thedistr-ictselector.102,*the loop circuit previously traced. throughihe .windings or' relay 122, through `the.Fwindings vof relayv 240 and, to battery and; ground aty the incoming selector 35,0 is opened-,and relay 240nbecomes deenergized. At its rmature-and back contact, relayv 240now `establishes a circuit over the left contacts ofcam,242,1through the winding.v of. relay 202 jto battery at theright contact :of cam. 201 causing `the energization of relay- 202 which, at-its armature and contact, establishes a circuit ,over the lower. contact of cam 212 to battery thro-ugh. the let'twinding of relay-213. Relay 213 thereupon energizes, advancing seque-nce switch 200 out ot' position 10 into position 13v and as its left armature and ffrontcontact closes a circuit Vfor energizing relay- 207; Thisfcircuit may be traced from battery througlnthe Awindingof relay 207, the lett `contacts otcain 229, left armature andXV frontgcontact of relay 213V to ground at the left-contact `of cam -231. After sequence switch 200 leaves .position 10, relay 213 ia maintained energized-,over the circuit. extending. through itsleft ernia-ture and` front Contact, the upper contact-,cfa cam 281, the left armature Aand baclrcontact of r'elay 243 tol ground. at the lower contact of -cain 228 and being energized when `sequence switch 200 reaches position 13 4 the squence switch is immediately driven out of,v position 13 through .position 14 into-position 16. After sequence switch 200i leaves position 15, the last; traced ,locking circuit oi relay 213 is openedv attheupper contactof cam 231 but relay A213. is'` maintained; energized over its 'leftarmatureland rontcontact to ground at the lower-left contact of cam 231 until after the sequence switch leaves ,position-.16 and there-fore whensequence switch 200 reaches position 10, it is vdriven .into position 18 over .a circuit extending throughthe v lower contactof cam. 214 and the right armature and -front .Contact of relay 213.

llith sequence switch 200 in position 18, the circuits previously traced-for relays 207, 2,02 and. 240 are openedr and a circuit is established for the updrive magnet 244 for restorof cam` 211., lhen'the switch shaft reaches normalposition,l a circuit lis closed for advancing; lsequence switchA 200 Tinto. its normal position, which cireuitmay be traced from battery through the magnet winding of sequence switch y200 upper right contact `of cam.- 21,4, commutator segment 245, shaft wiper22l2 thence to ground atrthe lower right contact of cam220.i Ally apparatus of the.,omeeselector250xis now in, normal positiont and the incoming, selector 350 and linal selector y 360, are thereupon released 'in the usual manner.

Overflow.

1t dur-ing trunl;y hunting,`the office selector 250 goes to an overflow position upon ,tinding all, trunks o'lla group busy, theshaft wiper-247 will rest upon an open porti-en of thel overflow segment Q 246 and` therefore, no ground ypotential willl be connected through thetest brush 230 over the back contact of relay-213 and later overftheupper right contact yof cam `220,` aspreviously traced. rlChis provisionlis made in order that two or more unitsoften trunks each may be formed into one trunk ,group by grounding the overflow sleeveof the intermediate unit, leaving only the overflow sleeveA of the final unit ungrounded, thek final sleeve then becoming the overflow. point for the entire group. The hunting movement of the .selector is conducted through the intermediate points by ground encountered on such points by the test brush 230y thence. over the lower right and upper left contacts of cam 229, the front contacts of the lett armature of relay 213 to battery through the winding of relay 213. lllhenthehnal overflow point is reached the test brush 230 encountering no ground potential, relay 213 deenergizes advancing sequenceswitc-h200 into position7. 1n position7 `a circuit is closed for relay 213 which may be traced from battery through the left winding-of relay 213, the upper right contact of cam 225, commutator segment 249, shaft wiper 217 thence to ground at the lower right contact of cam 220. Relay 21S thereupon energizes advancing sequence switch 200 out .of position 7 into position 10. Relay213 deenergizes asv soon as the sequence leaves position 7. Y

Inpassing.y through positions 8 and 9, a circuitis established for relay 243 extending through the right winding of this relay, the upper contact of cam 24S, conductor 219, segment 249, shai't wiper 217 to ground at the lower right contact of cam 220'. Relay-243 thereupon locks over its left winding and left arma-ture to ground at the lowerL contact ot cam 228, being maintained energized until the sequence switch leaves position 15. As soon as sequence switch 200 reaches position 10, the previously traced circuit for rel-ay .is 4again established over the upperl right contact ot cani 225 and relay 213 again advances sequence switch 200 out ot position 10 into position 13.V its sequence switch 200 passes through position 11, a circuit is established for relay 20T, extending from battery through the winding ot this relay, the lower lett contact et cani 201, winding ot relay 202, the upper right contact ot cani 203, conductor 219, segment 249, shaft wiper 217 to ground at the lower right contact ot cani 220. Relays 20'? and 202 are thereupon locked under the control ot relay 202 over the upper right contact ot cani 212 until after the sequence switch leaves position 111. lilith relay 20'! operated, when the sequence switch 200 reaches position 13, relay 233 is connected in a loop with the sender over conductors 109 and 110 in a circuit which inay be traced in part roin y conductor 110 through the inner right armature and front Contact of relay 207, the upper lett and loweright contacts of cani 208.I resistance eleinent 2011, relay 233, the lower contacts of cani A238 to battery, and troni conductor 109' through the outer right armature and front contact of relay 201 the lower left and upper right contacts ot cani 203, resistance element 210', the upper contacts ot cani 235 toground at the right armature and back contact ot relay 213. The overflow relay ot the sender is operated in this circuit, establishing the usual overflow condition at the sender and district selector and polarized relay 233 is operated shunting relay 202 in the manner previously described. As soon as the circuit traced from the sender through the winding of relay 233 is opened at Athe sender following the establishment oit the overflow condition, relay 207 deenergizes, connecting the windings ot relay 24-.0 in a circuit extending back to the sender and to batter)v through the left contacts ot cam and-to 2ground through the lower lett and upper right contacts of cani 235 and the right armature and back contact ot relay 213. i Then the district selector 102 reaches trunk closure position, relay 2-'1-0 energizes, closing an operatingcircuit for relay 213 extending' over the lower contact ot' cani 225, to battery through the lett winding'` of relay 213. Relay 213 thereupon opens the circuit ot relay 24-0 and at its rightarn'iature and trent contact closes a circuit tor advancing sequence switch 200 out ofi position 13 into position 14. lilith relay -2f-10-deenergized when sequence switch 200 reaches position 14:, the circuit of relay 213 is opened but this relay again en-.

ergizes soon as interruptor 251 closes its lower contact. The circuit of relay 213 may new be traced troni ground through interrnpter 251, lower right contact of cani the right arniature and contact ot relay 2-1'3, the upyier left contact of cani 232 to battery.' through the right winding oi relay 213. Aelay 213 upon energizing),l now a li'ances sequence switch 200 into position 1G.

ln position 10, relay 207 is intermittently operatei by the interruptor over the lelt contacts o1 cani 253, intermittently connectinp, battery through the lett contacts ot cam 23S and ground through contacts ot cani and right armature and back contact ot relay 213 lor producing' a liashing signal at the district link in case the connection has been established through a semi-inechanical operato1"s position. Relay 240 is maintained energized over the loop circuit extending to the district selector until the district selector is released, whereupon it deenergizes, closing a circuit over its arniature and back contact, the lett contacts ot cani 242 through the winding` o1 relay 202 to battery at the right Contact of earn 201. `Ylelay 202 energizcs in this circuit, establishinrg a circuit over the lower contact of cani tor cnengizingg` relay 213, which in turn aorances sequence switch 200 to the releasinnl position 18 in which position the incoming selector is restored as previously desclxhed.

Tell-lolo.

tlhould the incoming' selector go to the tell-tale position which is on the top of thc baul-z, during any selective movement as would happen it the updrivc magnet becomes stuclav and tails lo release, a circuit is established for sequence switch 200 over the rip'l t contacts o." cani 212, tell-tale segnient i shat't wiper to ground at the lower r ht contact ol' cani 220 or upper contact o1 cani 210, and sequence switch 200 is thereupon advanced out ol the selection posit-ion 2, -1v or (5, in which it may he standing. into position 10. The circuits ot the incorningr selector thereupon function as on an overflow condition except that relay 213 is energized over the contact of' relay 202, which is at this time energized over the lower lel't and upper right contacts ot caln 212. connnutator segment 251. shaft wiper 222 and `jround at the lower right contact of 'raln 220.

Release of selector upon, circuit'fallu-rc.

The ollice selector on account of faults, inoinentary zground or short circuits nlay be .st-uct: with its sequence switch 200 in position 3 following brush selection with ils shaft ol'lq nornial. To `guard against this condition, the interruptor 251 is provided. lilith sequence switch 200 in position 3, when the interruptor 251 makes its contact, a circuit is established over the lower lett Contact ot cani 248 to battery through the right winding' of relay 2113 which locks over its lett wir-udine' and left 'grinature to ground Cil at the lower Contact of, cam 228 until the sequence switch is advanced out of position 3@ lf the sequence switch 200 is still in position 3 after a period of two seconds, interrupter 251 makes its lower contact thereby establishing a circuit over the lowerright contact of cani 255, the right armature and contact of relay 243, the lower right and upper left contacts of cam 253 to battery through the winding of relay 207. Relay 207 `thereupon energizes and locks to ground over its left armature and left contact of cam 228.. until sequence switch 200 leaves position. 4. lith relay 207 energized and sequence switch 200 in position 3, a circuit is established for the down drive magnet 244 which may. be traced'from battery through. magnet 244, upper right and lower leftcontacts of cam 229, to ground through the left armature of relay 207 and the left contact of cam 228. Then the switch shaft reaches its normal position, the sequence switch 200 is, advanced out of position 3 into normal position in the usual manner. In position 3% and 4 ofthe sequence switch, with relay 207 energized, ground is connected to conductor 109 over the outer right armature and front contact of relay 207, the lower contacts of cam 20S, Vresistance elements 209, 210 and the left contact of cam 211 and battery is connected to conductor 110 over therinner right armature and front Contact of relay 207, the left contacts of relay .206,1 resistance elements 205 and 204, they lower contact of cam 203, relay 202 to battery at the right Contact of cam 201. This circuit is established for transmitting an. impulse of reverse current to the sender forregistering the overflow condition thereatr Y lf the oiiice selector is in the selection beyond position 7 and there is an open circuit on the trunk seized or the polarized relay 233 fails .to function, the selector may not be advanced into the talking position 10. To guard against this, the interrupter 256 is provided which closes a circuit over the right Contact of cani 248 to battery through theright winding of relay 243 as soon as the interrupter makes its Vleft contact. Relay 243 upon energizing locks over. its left armatureand contact to ground at the lower contact of cam 223 until the sequence switch leaves position 7%. If the` sequence switch has not advanced out ofposition 7% fifteen seconds after, relayL 243 energized, interrupter 256- makesv its upper contact, establishing a. circuit over theleft contactv of cam 255, right armature and contact of relay.. .243,. the upper leftcontact ofcam 232 to battery through right winding of relay 213. Relay 213 thereupon energizes, advancing sequence switch 200 out of position 7 into .position 10. Relay 213 uponenergizingalso mantainsrelay. 243 locked between vosition 7 and 9, over a circuit extending .rom ground through the right armature and front contact offrelay 213, left contact of ca1n216, left armature and front contact and left winding of relay 243, so that when sequence switch 200 reaches position 9, relay 243 is maintained locked over ythe lower contact of cam 228 until the sequence switch. loaves position 15. As soon as the sequence switch leaves position 9, relay 213 releases since with relay 243 locked, relay 213 cannot lock itself over the upper contact of relay 231 and the left armature and back contact of relay 243 when sequence switch 200 reaches position10. ln position 10 with relay 240 cle-energized, a circuit is established from ground through the armature and back contactof relay 240, left contacts of cam 242, winding of relay 202 to battery at the right contact of ca1n201 for energizing relay 202 which. in turn causes the energization of relay 213 and the advancey of sequence switch 200 out ofv position 10 into position 13. From this point the ,circuits of the selector connection with the overiiowcondition.

The selector which has been advanced to position 13 by the timing interrupter 251 may find. an open circuit toward the sen-der and cannot advance further. In this case, interrupter 251 closes a circuit: over' the lower .right contact of cam 214 for advancing sequence switch 200 into lposition14. In position 14, a circuit is thereuponA established for relay 21.3 Voverthe lowercontact of interrupte-r 251, lower right'contact of cam 255, right yarinatureand,contact of relay 243, relayz'243 havingoperated 4upon the previous operation, of interrupter 251 when the sequence switch was in'position, then through thenpper, left contact. of cam 232 to battery` through'right winding of relay 213. Relay 213 upon energizing.;4 then, advances sequence. Switch 200 out of position 14 into position. 16.., Inposition 16, unless relay 240 has operated, relay 202 again operates, in `turn ,operating relay 213y and advancingsequence switch 200 into releasing position 18. 4 l

Relayf240E islmademsensitive in order to function in positions.7 `through 10 Overloonnections extended, to` relay, call indicator trunks .operating on 24 vol'tspotential and therefore vits springs cannotbe made, stiff enough to always insure release on a high resistance trunkunder the overflow conditionV in position .16 .of sequenceswitch 200 when` 48 volts is `supplied tothis circuit. In position 16,., therefore, the. interrup.ter r256 is arranged to operaterelay 243Qoverthe right contact of cam 248 and.15.seconds later to close a circuit overtheleftl contactof cam 255, right armature and. contact of relay 243, the upper left contact of cam 222 to battery through the lright winding of reswitch function as previously described in 90 lay 213 for energizing relay 213 and advancing sequence switch 200 out of position 16 into the releasing position 18.

`It 'the calling subscriber A initiates a connection to the line ot the subscriber C in a manual call indicator ottice Z, the line switch 101, district selector 102 and otlice selector 250 function in the manner previously described up to the point where the sequence switch ot' the otiice selector advances into the selection beyond position 7, except that the brushes ofthe otiice selector 2504 are set to seizea trunk extending to the office Z,

l it being assumed that the trunk 257, 258 is at the time idle and is taken for use. At the oice sender since the call is of the relay call indicator class and the code registers have registered that fact upon the class switch ot the sender, a circuit becomes closed tor relay 125 associated with the call indicator impulser 100, which circuit may be traced from battery, through the winding of relay 125, outer right armature and back contact of relay 123 to ground at the lett contact of cam 126 of the control switch 114. Relay 125, upon energizing, locks over its inner upper armature and contact, through rcam contact 128 to ground at the right contact of cam'126, remaining locked until the impulser switch 100 leavesposition 8.

Following the seizure of the trunk 257, 258, a control circuit is established from the sender 'to the control relay 313 of the trunk circuit which may be traced from battery through the right winding of relay 313, the normal right contacts of relay 314, the upper lett winding of repeating coil 314, the outer right back con'tact of relay 316, conductor 257, brush 236, the lower right and upper lett contacts of cam 225, resistance ele ment 210, the upper right and lower` lett contacts of cani 208, the outer rih't armature and front contact of relay 207, conductor 109, the upper brush of switch 102, lower contact of cam 111, wiper 112, cam contact 113, lower contact of cam 115, relay 116, winding of relay 130, right contacts of cani 118, contact of cam 119, wiper 120, lower brush ot switch 102, conductor 110, the inner right armature and front contact of relay 207, upper lett and lower right contacts ot cam 206, resistance element 204, winding of polarized relay 233, right contacts of cam 238, brush 239, conductor 258, inner armature and back contact of relay 316, lower left winding of repeating coil 315, normal lett contacts of relay 314 to ground through the left winding of relay 313. Relay 130 and 313 energize in this circuit, the current, however, flowing in the wrong direction to cause the energization of polarized relay 233. Upon the energization oi relay 130 the sender sequence switch is advanced out ot' position 12 in which it is standing following the completion of office group selection into position 11i in the manner fully set forth in the patent to F. A. Stearn hereinbefore referred to. ln position 14 an obvious circuit is established Yfor relay 123 over the contact of cani 124;, whereupon the initial energizing circuit of relay 125 is opened. Relay 313, upon energizing, closes 'the circuit of relay 317 which locks over its inner right armature contact independently ot' relay 322 and closes an obvious circuit for the lamp 318.

The operator noting the illumination oit' lamp 318 depresses the display lrcy 319, thereby establishing a circuit from battery at the outer right contact ot sleeve relay 324, through the right winding of relay 320, the lett armature and front contact of relay 317, contact of key 319, armature and back contact of relay 420 to ground at the left armature and baclr contact of relay 408. Relay 320 locks through both of its windings and closes obvious circuits 'or relay L05 oi the call indicator control circuit. and 1`or relay Relay 322, in turn, closes a. circuit for relay 323 which locks in series with relay Relay 325, however, being shunted remains deenergized as long as relay 317 is energized. Relay 323 at its left armature contact also closes a circuit through the windings of relays 316 and 420 in series, relay 316 disconnecting the windings ot' relay 313 from trunk conductors 257 and 258 and connecting these trunk conductors to the impulse leads 331 and 332 extending to the indicator control circuit. lVith relay 313 disconnected and deenergized, the circuit of relay 317 is opened, removing the shunt from around the winding of relay 325 which thereupon energizes in the locking circuit of relay 323. At. its back contact relay 317 connects the lamp 318 in series with the interrupter 326 for fiashing the lamp until the display of the wanted line number is completed on the call indicator and the operator in response thereto has extended the connection to the wanted line. At the indicator control circuit upon the energization of relay 405 ground is connected to the conductor 406 for furnishing operating and locking ground potential to the several control and registering relays of the call indicator.

At the otlice sender when relay 316 ener gized and opened the circuit previously traced through the windings of relays 313 and 130, relay 130 deenergized thereby coinpleting a circuit over its right arniatiu'e and back Contact, through the inner right armature and front contact ot relay 123, contacts of cam 128 to battery, through the winding of relay 127. Relay 127 thereupon energizes closing .a circuit from ground over its armature contact, the lowfermo'st armature ,and front contact of relay '125, contact of cam 129 :to battery through the ina-Tnet winding of the impulser switch 100 for advancing the impulser switch out of position 1, through position 3. VAs soon as the switch 100 leaves position 3 the locking circuit oat relay 125 is opened so that when switch 100 rotates around into position 1, it finds no oper-ating circuit and is arrested aft-er completing a single revolution. VVh'en passing through a complete revolution switch 100 transmits a plurality of se-ries of cozde impulses to the call indicator of Fig. 4 in the well-known manner, a series being transmitted for each digit of the line designation. YWith relay 123 energized and relay 130 lde energized, the circuit over which the code impulses are transmitted may be .traced from conductor 133, upper armature and rontco'ntact of relay 125 orthe contact cam 135, inner left armature and back contact or' relay l130, inner left armature and front "Contact of relay 123, upper contact of cam k115 Contact of cam 113, thence as previously traced to conductor 257, outer armature and front Contact of relay 316, conductor 332, inner right armature and hack contact of relay 410-7 winding of positively polarized relay 400, winding of negatively polarized relay 401, winding of marginal relayl 40,2, outer left armature and back Contact of relay 410, conductor 331,

' inner armature 'and front contact of relay 316, lconductor 258, thence as previously traced to Vwiper 120,.conta'ct of cam 119', outer left armature and contact of relay 123, outer left armature -and hack contact of relay 130, inner lower armature and contact off relay 125 or the upper Contact of cam 136, to conductor 134. The nnpulses of ea-ch 'series may consist, in the usual manner, of light positive and light and heavy negative impulses.

Since lall of the positive' impulses are light, the marginal polarized relay 233 which is included in the impulsing circuit does not respond. In response to impulses of each series relays 400, 401 and 402 selectively operate and in conjunction with relays 403 and 404 cause the operation of the usual recording` relays (not shown). In the well-known manner the pairs of transfer relays such as 411, 412, 413, 414, 415, 416, 417, 410, 427 operate upon the transmission of successive series of impulses until relay 427 operates upon the transmission of the lastpser'ies of impulses. Nhen relay 427 operates it locks to conductor 406 in series with relay 410, but relay 410 does not operate in this locking circuit until the completion of the last series of impulses- When the last series oit impulses is terminated and relays 403 and 404 both become deencifgized, relay 410 operates opening the previously traced impulsi-ng circuit through the windings of relays 400, 401 and 402, closing anew circuit extending from conductor 322, over the inner right armature and front contact of relay 410, winding of nega-tively polarized relay 401, conductor 418, outer lett 'armature and front contact ot' relay 410 to conductor 331. lt is to be noted that the operation otrelay 410 has been instrumen-tal in lcr-.tting relays 400 and 402 from the pulsing` circuit, over conductors 331 and 332 for reducing the resistance of this circuit and in` reversing relay 401 in the circuit so that it will respond to positive impulse. The resistanceof the circuit is additionally reduced by the connection of resistance 419 in parallel with relay 4.01 through front contacts of relay 410. At the sender upon the completion of the trans-mission or the code impulses and the return .of switch 100 to position 1, a 'circuit was closed for translator control sequence switch 114 for fadvancing it out of position 9, the circuit eX- tending over the contact of cam 137, Contact oi cam 139, lowermost armature and back con-tact of relay 125 to ground at the armature and iront contact or relay127. As the switch 114 advances from position 9 through position 91/2, a. circuit is closed for transmitting a heavy impulse of positive current over the iinpulsing circuit previously traced through the winding of relay 233 and the winding orP polarized relay 401. At

the sender this current flows from battery over cam contact 138, cam contacts 140, the upper armature and back contact of relay 125, thence over the circuit traced through the windings of relays 401, and 233 returning over the lowermost contact of cam 136 to ground at the right contact of cam 126. Relay 401 energizes closing a circuit from ground on conductor 406, through the conta-ct of relay 401, inner left armature and front Contact of relay 410 to battery through the winding of relay 421. Relay 421 therepon 'closes a circuit from ground'at the outer contact of relay 417, which relay energized during the transmission of the tens series of code impulses, the outer right armature and contact of relay 427, left armature and contact of relay 421, winding of relay 408 to battery through the winding of relay" 421. is soon as the heavy positive irnpulse through relay 401 -ceases, relay 403 energizesin the locking circuit of relay 421 opening` at its right armature and bach contact the Vcircuit oi' relay 316. Relay' 316 thereupon deenergizes, disconnecting the impulse leads 331 and 332 from the trunk conductors 257 and 258 connecting these trunk 'conductors to the windings of relay 313. Upon the transmission ot the heavy posit-ive impulse to the relay 401, relay 23 receives current in the proper direction and of sufficient strength to cause its energizetion, whereupon sequence switch 200 of the otlice selector 250 is advanced into the tall? wanted line number upon the lamps of the indicator inserts the plug 327 in which the trunk circuit terminates, in the jack 328 of the indicated line, whereupon relay 324 energizes, opening the holding circuit of relay 320, which in turn, opens the circuits of relays 322 and 405. Relay 322 functions to disconnect the lamp 318 from the interrupter 326, and relay 405 removes ground potential from the conductor 406, permitting the restoration of all operated equipment of the call indicator. The apparatus at the oihce Z then functions in the usual manner to call the wanted subscriber and to control supervision upon the subscriber-s response and following the termination of the conversation. Upon the completion of the conversation between lines A and C the line switch 101, district selector 102 and office selector 250 are released in the manner previously described, and the operator at office Z receiving the usual disconnect signal displayed on lamp 329, removes plug 327 from the jackf328, thereby releasing the apparatus at her position.

`Had the call been established to the oiiice Z from the oice W, over an oliice selector of the three-wire type, such as disclosed in the aforementioned patent to F. A. Stearn, no heavy positive impulse would be required to advance the otlice selector to the talking position and, therefore, the sender at such office would not be equipped to transmit such a positive impulse following the completion of the transmission of call indicator impulses. In this case following the registration o-f all call indicator impulses at the call indica-tor of otlice Z and the energization relays 410 and 427, relay 408 is automatically energized through the operation of timing relays 422 and 42?) for disconnecting the indicator from the trunk circuit through the operation of relay 31.6. Relays 422 and 423 function in the folle-wing manner. Then relay 417 energizes during the transmission of the tens series of impulses, a circuit is established over its contact, the left armature contact of relay 423 to battery through the winding of relay 422 and relay 422 energizes. During the transmission of the units series of impulses relay 427 energizes closing a circuit from ground at the contact of relay 417, through the outer right contact of relay 427 to battery, through the winding of relay 428. Relay 423 energizes, opening the circuit through relay 422. After an interval measured by the releasing time of slow releasing relay 422, a circuit is established from ground at the back contact of relay 422, the right contact of relay 423, windings of relay 408 and 421 to battery. Relay 408 thereupon energizes opening the circuit of relay 316 disconnecting the call indicator cont-rol circuit from trunk conductors 257 and 258. The interval measured by the timing relays 422 and 423 is designed to delay the disconnection of the call indicator control circuit from trunk 257, 258 for a period sufficient for the reception of a heavy positive pulse where one is required.

lifhat is claimed is:

1. In a telephone exchange system, a trunk, a selector switch for extending a connection therefrom, control means forsaid switch, a control circuit extending thereto over said trunk, means for further extending said connection, means at said switch for disassociating said control circuit from said control means and for extending it to said connection extending means, and means at said switch for compensating` the resistance of said control circuit incident to the extension of said circuit.

2. In a telephone exchange system, a trunk, a selector switch for extending a connection therefrom, control means for said switch, a control circuit extending thereto, over said trunk means for further extending said connection, means at said switch for disassociating said control circuit from said control means and for extending it to said connection extending means, resistance elcments, and means for Variably connecting said elements into said control circuit for compensating the resistance thereof during the conn iction thereof to said control means and to said connection extending means.

3. ln a telephone exchange system, a trunk, a selector switch having a plurality of stages of operation, means for extending a connection over said trunl; to' said switch, means for operating said switch in certain of its stages to iurthcr extend said connection, other connection extending means cetrollable over said trunk in another' stage of operation of said switch, resistance elcments, and means at said switch for variably connecting said elements into said trunk in different stages of operation of said switch,

4. ln a telephone exchange system, a trunk, a selector switch, means for extending a connection over the trunk to said switch,

liary switch haring a series of positor controlling said selector switch in operation, means for operating the switch caf ` ri ably ici- certain positions of said auxiliary switch to inrther extend said connection, other connection extending means controllable. over said trunk in a certain position ot said auxiliary switch, resistance elements, and means controlled by said auxiliary switch for vaconnectin'g said elements into said loin dili'erent positions of said auxiliary switch.

5. In a telephone lexchange syst-ein, a se- 'e'ctfor switch :For extending talking connections, two conductoil trunks 'extending thereto and thereiron'i, means toi' Afurther exending said connections, controlliiifg mechanism Aor said switch to be sequentially advanced through successive positions in the operation or said switch, andtnie'ans controlliable over said two conductor trunks serially incident to the operation ot said connection extending means tor advancing said mechanism to a given position.

6. ln 'a telephone exchange system, a selector switch for extending talking connections, i

two conductor trnnks extending thereto and therefrom, ineens for further extending said connections, 'controlling meclranisn'i for said switch arranged to be sequentially advanced through successive positions in the 4operation el? said switch and to rest in a Given position during the control of said connection 'extending means, and means controllable over Vsaid two conductor trunks serially incident to the operation ot said connection extending means for advancing said mechanism to a position -in which the talking circuit is established through said switch.

7. In a telephone exchange system, a selector Vswitch for extending talking connections, two conductor trunks extending thereto and therefrom, means tor further extending said connections, controlling mechanism i`o`r said switch arranged to be sequentially advanced through successive positions in the operation 'oi' said switch and to rest in a given position during the control of said connection extending means, and a polarized relay controllable over said two conductor trunks incident to the operation or said connection extending means tor advancing said mechanism to a position in which a talking circuit is established at said switch.

5%. ln a telephone exchange system, a selector switch for extending talking connections, twoA conductor trunks extending thereto and theretron'i, means ttor further extending said c'oijmectio'ns, controlling mechanism tor said switch arraiiged to be sequentially advanced through successive positions in the operation oil said switch and to rest in a given position during the control said connection extending means, a polarized relay at said switch arranged for insertion in series relation with said trunks lby said controlling mechanism in said given position, `and means incident toL the oper-ation of said lconnection extending means for operating said relay to advance said mechanism to a position in which a talk-v ing said connections, controlling. mechanism.

tor sai-d 'switch arranged to be sequei'itially advanced through successive positions in the operation of said switch and to rest in a given position during the operation of said connection `extending means, a polarized relay at said switch arranged for insertion in seri-'es relation with said trunks in said given position of said mechanism, means for transmitting a heavy pulse ot current of the proper polarity for operating` said relay to establish a talking circuit at said switch, and a vsecon-d relay included serially in said talking circuit Jfor controlling thev further advance 'of said mechanism.

l0. In a telephone exchange system, a selector switch tor extending talking connections, two conductor trunks extending thereto 'andthefreironn means tor turth-er extending said connection, controlling mechanisn'i ior said switch arranged to be sequentially advanced through successive positions in the operation of said switch and to rest in a given position during the operation oi' said connection extending means, a polarized relay at said switch arranged tor insertion in series relation with said trunks in said given position of said mechanism and irresponsive to connection controlling impulses transinitt-ed therethrough, a sender for controlling the operation of said switch and said connection extending means,rand means at said sender operative upon the completion or its control of the extension of said connection for transmit-ting 'an impulse of current or proper polarity :tor operating said relay, whereby said mechanism i's advanced to establish la talking circ-uit at said switch.

ll. In a telephone exchange system, a selector Aswitch for extending talking connections, two conductor trunks extending thereto and therefrom, and means 'controllable over said trunks serially tor further extending said connections.

ln witness whereof, l hereunto subscribe my name this 9th day oic August A. D., 1923.

Lewis n. Jonsson. 

